The present invention relates to a rubber ring for a gasket used for ensuring a sealing property in a local portion of a gasket such as a fluid hole and the like of the gasket, and wherein an annular sealing rubber has been connected to a hole edge portion of a metal plate.
In order to improve the sealing property between a cylinder block and a cylinder head, an internal combustion gasket such as an automobile engine and the like is installed between the cylinder block and the cylinder head. In the gasket, there is provided the fluid. hole such as a water hole for passing coolant water, an oil hole for passing oil, and the like in addition to a combustion chamber hole opening in a combustion chamber of the cylinder block, and a bolt hole for inserting and passing a bolt which fastens securely the cylinder block and the cylinder head.
The rubber ring for a gasket is used for mainly ensuring the sealing property of the fluid hole and the like of such a gasket. In the rubber ring for a gasket, the hole edge portion of the metal plate is embedded in an end face on an outer circumferential side of the annular sealing rubber, and the aforementioned sealing rubber is attached to the hole edge portion. When the rubber ring is provided in the fluid hole and the like of the aforementioned gasket, the metal plate of the rubber ring is placed between gasket plates on both upper and lower face sides of the gasket, and the rubber ring is installed in a circumference of the liquid hole and the like. Then, when the gasket to which the rubber ring is provided, is installed between the cylinder head and the cylinder block, in the circumference of the fluid hole, the sealing rubber of the rubber ring is pressed by the cylinder head and the cylinder block, so that the sealing property of the fluid hole is ensured.
FIG. 6 shows a cross-sectional shape of substantial parts of a rubber ring for a gasket which has been conventionally used, as an example. A rubber ring 50 shown an FIG. 6 includes an annular sealing rubber 51, and a metal plate 52 including a hole having a shape which fits into the fluid hole and the like. A planar shape of the sealing rubber 51 corresponds to the shape of the hole of the metal plate 52. The hole edge portion of the metal plate 52 is embedded from the end face on the outer circumferential side of the sealing rubber 51, and the sealing rubber 51 is attached to the hole edge portion of the metal plate 52. The cross-sectional shape of the rubber ring 50 has a shape symmetrical to a center line L in a thickness direction thereof. Also, the sealing rubber 51 of the rubber ring 50 comprises a seal portion 54 including a thickest portion which has a largest thickness, and an attachment portion 55 relative to the metal plate 52, which is sloped such that a thickness diminishes as the thickness goes to the outer circumferential side.
FIGS. 7(a) to 7(c) show results of stress distributions when the rubber ring 50 for a gasket is sandwiched by two faces pressing from up and down, and is compressed only by 20%, 25%, and 30% in the thickness direction. A dimension of stress inside the rubber ring 50 is expressed using a contrasting density of dots, wherein as the density is paler, in an order of symbols A, B, C, and D, the stress becomes larger.
In a case wherein the rubber ring 50 is compressed only by 20% to 30%, a nearly whole surface of the sealing rubber 51 contacts with he upper and lower two faces pressing the rubber ring 50. The stress inside the sealing rubber 51 becomes large near a portion wherein the sealing rubber 51 has contact with the upper and lower two faces, and especially, in a case of FIGS. 7(b) and 7(c) wherein. the rubber ring 50 is compressed by 25% or above, the stress becomes entirely large even near an attachment interfacial surface between the metal plate 52 and the sealing rubber 51.
Referring to such stress distributions, in the aforementioned conventional rubber ring 50 for a gasket, when the rubber ring 50 for a gasket is used in a state in which a pressure is applied by placing the rubber ring 50 in the gasket, due to a deformation of the sealing rubber 51, the stress in the attachment interfacial surface between the sealing rubber 51 and the metal plate 52 becomes large. Consequently, in a case wherein the aforementioned gasket is used for a long period of time, a detachment of the sealing rubber 51 from the aforementioned metal plate 52 may occur, or a crack in the sealing rubber 51 may occur in a vicinity of an end portion of the metal plate 52, so that the above-mentioned detachment or the crack may develop so as to be easily damaged.
Also, FIG. 8 shows a cross-sectional shape of substantial parts of another rubber ring 60 for a gasket shown as a. reference example. As in a case of the rubber ring 50 shown in FIG. 6, the rubber ring 60 includes an annular sealing rubber 61, and a metal plate 62 including a hole having a shape which fits into the fluid. hole and the like of the gasket. The sealing rubber 61 comprises a seal portion 64 including a thickest portion which has a largest thickness, and an attachment portion 65 relative to the metal plate 62, whose outer face is sloped such that a thickness diminishes as the outer face of the attachment portion 65 goes to an outer circumferential side more than the example of FIG. 6
FIG. 9 shows a stress distribution when the rubber ring 60 of the aforementioned reference example is sandwiched. by two faces pressing from up and down, and is compressed by 30% in a thickness direction as in the case of FIG. 7(c). A dimension of stress inside the rubber ring 60 is expressed. using the same indication as FIGS. 7(a), 7(b), and 7(c).
Compared to the case of FIG. 7(c), as for the stress distribution shown in FIG. 9, in the rubber ring 60 of the reference example, a thickness of the attachment portion 65 relative to the metal plate 62 is sloped to diminish as the attachment portion 65 goes to the outer circumferential side more than the example of FIG. 6, so that a most part of the attachment portion 65 does not contact with the upper and lower two faces pressing the rubber ring 60. Inferably, from that reason, when the rubber ring 60 is compressed by 30%, the stress inside the sealing rubber 61 does not increase in a portion wherein the sealing rubber 61 does not contact with the upper and lower two faces. However, in a vicinity of an end portion of a hole edge portion of the metal plate 62 embedded in the sealing rubber 61, the stress becomes relatively large. This is considered to occur because an effect of a compression force acted on the seal portion 64 of the sealing rubber 61 affects the attachment portion 65 which is integrated although the thickness gradually diminishes from the seal portion 64.
Based on knowledge regarding the stress which acts on an inside of the sealing rubber in the aforementioned rubber ring, a technical object of the present invention is to provide a rubber ring for a gasket, which reduces the stress occurring near the attachment interfacial surface of the sealing rubber and the metal plate when the rubber ring for a gasket is compressed so as to be capable of controlling an occurrence of the detachment of the sealing rubber from the metal plate, or the crack in the sealing rubber in the vicinity of the end portion of the metal plate due to long periods of usage.
Further objects and advantages of the invention will be apparent from the following description of the invention.